1. Field of the Invention
This invention generally relates to an amplifier circuit that utilizes a semiconductor device in which GaN or a GaN compound semiconductor element (hereinafter, referred to as GaN-based semiconductor device) is employed for an active region.
2. Description of the Related Art
These years, the GaN-based semiconductor devices such as FET or HEMT that includes GaN, AlGaN, or InAlGaN, which attract attention, enable a higher output than other devices that include Si or GaAs. For example, the GaN-based semiconductor devices are expected to apply to mobile telephones or base stations of the mobile telephones, as described in Japanese Patent Application Publication No. 9-246471.
In order to put the GaN-based semiconductor devices to practical use, it is important to grasp the specific characteristic. However, actual studies of the GaN-based semiconductor devices have recently started and there are still many unknowns at present.
The inventor of the present invention has found that a positive phase distortion occurs on the GaN-based semiconductor device. Generally, it is ideal that an amplifying device amplifies the input signal to maintain a constant phase difference between the input and output, regardless of the relationship between the input signal and output power. However, on the GaN-based semiconductor device, the phase of the output signal is distorted as the output power increases, as shown in FIG. 1. There has been no proposal for the method of correcting the phase distortion in the amplifier circuit having the GaN-based semiconductor device.